The field of the invention is systems and methods for x-ray phase contrast imaging. More particularly, the invention relates to systems and methods for x-ray phase contrast imaging using a coded-source imaging technique.
Coded aperture imaging has been proposed in the past as a means for improving the spatial resolution, sensitivity, and signal-to-noise ratio (“SNR”) of images formed by x-ray radiation. For many imaging applications, coded aperture cameras have proven advantageous relative to other candidate systems, including the single pinhole camera and multi-hole collimator systems. In contrast to these other systems, for instance, the coded aperture camera is characterized by high sensitivity, while simultaneously achieving exceptional spatial resolution in the reconstructed image.
In contrast to the single pinhole camera, coded aperture systems utilize multiple, specially-arranged pinholes to increase the overall photon transmission, and hence the sensitivity, of the imaging camera. In operation, radiation from the object to be imaged is projected through the coded aperture mask and onto a position-sensitive detector. The coded aperture mask contains a number of discrete, specially arranged elements that are either opaque or transparent to the incident photons. The raw signal from the detector does not reflect a directly recognizable image, but instead represents the signal from the object that has been modulated or encoded by the particular aperture pattern. This recorded signal can then be digitally or optically processed to extract a reconstructed image of the object.
Coded-aperture imaging has its drawbacks, however, in that the improvement in imaging performance provided by the method depends on the nature of the object being imaged. Due to this, and counter-intuitively, the actual SNR improvement attainable with coded-aperture imaging may be better for aperture patterns that have a smaller fraction of open area despite the smaller fraction of available x-rays that are used. Because the imaging technique requires the use of one or more coded apertures that are radioopaque, many, photons that could otherwise be used to for imaging are left unused. This, in turn, lowers the potential SNR that can be achieved with coded aperture imaging, but as mentioned above, this depends on the nature of the object being imaged. Additionally, the coded aperture places limits on the field-of-view and angular resolution that can be realized. For instance, the angular resolution of the coded aperture imaging system is fixed by the aperture separation from the detector plane, the configuration of the detector array, and the aperture pattern. Coded aperture imaging systems are also limited in that they require fixed apertures and thus can only vary their detection gaze by physically adjusting the relative positions of the x-ray source, aperture, subject, and/or detector.
It would therefore be desirable to provide a method for phase contrast imaging that can utilize the advantages of coded-source imaging while improving on the limitations of currently available coded-aperture imaging techniques, including the reliance on a fixed, coded aperture that can lower attainable SNR and limit angular resolution.